Cobalt(II) triazene 1-oxide bis(chelates). A case of planar (low spin)–tetrahedral (high spin) isomerism

High- and low-spin cobalt(II) trizene 1-oxide bis(chelates) have been isolated. The low-spin complexes possess square-planar structure whilst the high-spin complexes are tetrahedral. The molecular structure of high-spin [Co(OMeN3C6H4Me-4)2] has been determined: triclinic, space group P, Z= 2, a= 7.970(5), b= 10.174(5), c= 11.676(5)A, α= 87.18(4), β= 74.31(4) and γ= 74.06(4)°. For some complexes the isolation of both planar (low-spin) and tetrahedral (high-spin) isomers or of their conglomerates is possible depending on the synthesis conditions. The crystal structure of square-planar [Ni(OMeN3C6H4-Me-4)2], which is isomorphous with the low-spin isomer of [Co(OMeN3C6H4Me-4)2], has been determined: triclinic, space group P, Z= 1, with a= 7.495(2), b= 7.694(5), c= 8.612(3)A, α= 64.64(5), β= 87.84(2) and γ= 78.64(3)°. The complexes exhibit a planar-tetrahedral equilibrium in non-co-ordinating solvents, the ΔH⊖ and ΔS⊖ values of which, determined from solution magnetic susceptibility measurements, are in the range 1–15 kJ mol–1 and 5–30 J K–1 mol–1, respectively. The electrochemical properties of the complexes are given.

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